Prof Ian Morison, a research haematologist in the Otago Department of Pathology, first heard about McCormick about 20 years ago.
As a child, McCormick was admitted to hospital with a B lymphocyte blood cell count 50 times higher than normal, and he underwent surgery to remove his enlarged spleen.
He then endured eight years of chemotherapy and for an even longer period underwent weekly blood tests.
But that was expected to be futile, with hospital clinic letters at the time describing how they were "doing their best to delay the inevitable termination".
Nevertheless, McCormick survived.
After getting sick of all the tests and procedures, which were making him sicker than his condition was, he decided to take off and he spent more than a decade on fishing boats.
When he returned to Dunedin he went to a doctor who, after seeing his test results, realised he did not have leukaemia after all. Prof Morison decided to make it his mission to solve the medical mystery.
Together with pathology colleagues Jackie Ludgate and Rob Weeks, he has done just that, and they now know exactly what went wrong with Mr McCormick's developing immune system.
"Ray carries a mutation in a gene called CARD11 that supercharges the growth of B lymphocytes, and the vast majority of these cells don't actually grow up to be fully functional," Prof Morison said.
While it was satisfying to solve a medical mystery, Prof Morison said in this case there was the added bonus that their studies of Mr McCormick's cells have revealed significant findings about how each B lymphocyte designs its unique antibody type and structure.
"Ray's CARD11 mutation allows the cells to survive when similar cells from a normal person would die. His cells reveal the mistakes that naturally occur during development.
"The immune system is immensely complex, and Ray's results have allowed us to dissect one small part of it and guide other scientists around the world as they study how our cells make antibodies."
A paper outlining the result has just been published in the Journal of Clinical Immunology.
Apart from the side effects of the chemotherapy, McCormick had always been reasonably healthy.
But his immune system was affected and compromised.
For example, it took him longer to shake off colds than other people.
He told the Otago Daily Times that he was unable to have children due to the medication he had taken when he was younger.
"That p... me off," McCormick said.
His misdiagnosis also put unnecessary pressure on his parents when he was young.
Despite the frustration, he was happy to be part of the ongoing research Prof Morison was doing.
"If it can help young kids out, I'm more than happy to do it."
He was also happy the truth was finally coming out after so many years.
"I'll just keep doing what I'm doing, one day at a time, and just keep on going.
"That's all you can do."